Norit

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Impala dark is a Norit: pattern (20 × 15 cm)

Norites are mafic plutonic rocks and are classed as hard rocks . They are similar in appearance, properties and composition to gabbros , but differ from them in that orthopyroxene predominates in the composition instead of clinopyroxene .

In petrography, rocks made of 10–90% orthopyroxene ( enstatite , bronzite , hypersthene ) and 10–90% basic plagioclase ( labradorite / bytownite according to the old classification) with less than 5% clinopyroxene ( augite ), olivine or quartz are called norites (35% -65% mafic ingredients). Accessories are e.g. B. ilmenite , magnetite and pyrrhotite . The corresponding rock 10–90% olivine instead of orthopyroxene is a troctolite .

use

Natural stone

Norite have technical properties similar to granite . Since these stones lack quartz , they are not as wear-resistant as the granites. These are often dark types of rock. Together with other dark plutonites such as gabbro , they are popularly referred to as "black granites" in the natural stone trade.

“Norite are gabbro rocks with certain pyroxene minerals; the orthopyroxenes outweigh the clinopyroxenes. There is no difference to normal gabbros in terms of technical and optical properties. "

Type of natural stone
  • Impala (Other names for Impala are: Nero Afrika, Rustenburg, Schwarz-Afrika)

Importance as a raw material carrier

Norite can contain finely distributed (disseminated) sulfides as liquid-magmatic excretion , such as pyrrhotite (magnetic gravel), pentlandite (nickel magnetic gravel) and chalcopyrite (copper gravel). If the nickel content is sufficient and the stocks are adequate, the rock then becomes nickel and copper ore. Examples in Europe: Lainejaur in Skelleftefeld in Sweden, Eptevann and Flat in Norway. Examples in Canada: Sudbury Basin in Ontario, Voiseau Bay in Labrador.

Individual evidence

  1. ^ W. Maresch, O. Medenbach: Rocks . Mosaik, Munich 1987, ISBN 3-576-10699-5 .
  2. Karlfried Fuchs: Natural stones from all over the world, discover, determine, use . tape 2 . Callwey, Munich 1997, ISBN 3-7667-1267-5 , pp. IX .
  3. ^ Walther E. Petrascheck , W. Pohl: Storage theory . 3. Edition. E. Schwizerbarth'sche Verlagsbuchhandlung, Stuttgart 1982, ISBN 3-510-65105-7 .